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How to subtract signals using lock-in-ampl

  1. Aug 10, 2011 #1
    i want to subtract photocurrents from two photodiodes. please tell me how to do this. also please tell me how to measure current and voltage with a lock in amplifier.

    Thank you very much
  2. jcsd
  3. Aug 11, 2011 #2


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    There are many ways to subtract two signals. Are you planning to design your own circuit (using an op-amp), or two use an instrument (such as a summing amplifier)?

    Can you be a bit more specific about the lock-in? Which model is it?
    Some lock-in amplifiers have a current input meaning measuring a current signal is easy.

    Measuring with a lock-in is also easy (but understanding what you are doing is a bit more tricky): connect the reference frequency to the ref input and the signal to the measurement input; set the sensitivity, reserve and time constant and the lock-in will show you the voltage/current.
    For more specific instructions I would suggest reading the manual.
  4. Aug 15, 2011 #3
    Thanks alot. well i am planning to do Homodyne detection. in this method, the photocurrets from two photodiodes need to be subtracted. there might be different ways to do this, the one that i want to do is to first measure both the currents using lock in. then feeding the ouput from lock in to storage oscilloscope, i want to subtract them and see the photocurrents difference. the lock in model is SR830.

    Thanks alot
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